AmdCpmDisplayFeatureSMM - SMM callout (AMD-SB-7027): MULTI-TENANT ISOLATION: An SMM callout

Impact

MULTI-TENANT ISOLATION: An SMM callout in the AmdCpmDisplayFeatureSMM driver lets ring-0 code overwrite SMRAM. SMM callouts are the classic UEFI escalation pattern: SMM code calls outward into memory the OS controls, so the OS supplies the code SMM then runs. Reported by Quarkslab, scored 8.2 with changed scope - the attacker crosses from the OS into the platform's most privileged context.

Who can reach it

Local, ring-0 on the host.

What to do

Fixed in AMD PI/AGESA firmware and delivered only as an OEM SBIOS package - AMD ships the PI drop to Dell, HPE, Supermicro, Lenovo and the ODMs, who each requalify before releasing BIOS. **Budget one to six months of OEM lag**, and note that several CVEs in this batch are marked 'no fix planned' on Naples (EPYC 7001) - for those the only remediation is retiring the hardware. Applying it means cordon, drain and a full power cycle per node; there is no driver reload, no live patch and no VBIOS step. Patch alongside the sibling AmdPspP2CmboxV2 issue in the same bulletin - they ship together and leaving one open leaves the class open.

References